Odell Beckham Jr., and a very expensive timepiece, in the Cleveland Browns season opener against Tennessee. (Photo credit: Getty Images)

LES BREULEUX, SWITZERLAND: Odell Beckham Jr.’s decision to wear a Richard Mille watch during the Cleveland Browns’ game against the Tennessee Titans last Sunday was as much a shock to the Swiss luxury watchmaker as it was to fans.

His "ultimate flex" became a Twitter Moment on Sunday and was covered by outlets including USA Today, The Washington Post, Business Insider and The Hollywood Reporter.

Mille doesn’t have an official partnership with Beckham, said Laura Hughes, director of communications for the brand in the Americas.

"He is a customer," Hughes said. "We knew he bought the watch, but we didn’t know he would be wearing it on Sunday."

Beckham is passionate about his Richard Mille timepiece. He has worn the $350,000 watch at events such as the ESPYs red carpet, on the cover of Sports Illustrated‘s NFL Preview and during a practice session.

He is also skirting the NFL’s rules about what players can wear on the field. The league prohibits players from wearing "metal or other hard objects that project from a player’s person or uniform." The league is planning to speak with Beckham Jr. about the watch, according to the Associated Press.

However, he plans to keep wearing the watch.

"I’m here to play football,’’ Beckham told media outlets. "I would love for them to talk about football and what I do on the field. If I messed up on the field or if I didn’t do well on the field, talk about my performance. Don’t talk about any extracurricular, that’s just it. If anybody else would’ve worn the watch, or if it was a $20 watch, it wouldn’t have been no problem.’’

Richard Mille isn’t trying to capitalize on Beckham’s insistence. Hughes said she has been confirming with media outlets that he was wearing a RM 11-03 McLaren Flyback Chronograph. The brand does not work with a PR firm.

"We only made 500 pieces of that particular watch for the world," she said. "In order to purchase it, it was only initially made available to people who purchased a specific model of McLaren automobile. Some of the car owners opted out, and those were made available for others to buy."

It’s normal to see an athlete sporting a fancy Richard Mille watch, just not a football player. Also last Sunday, Rafael Nadal beat Daniil Medvedev in the U.S. Open Tennis Championships while wearing a more expensive $725,000 Richard Mille timepiece on his wrist. Nadal has been a Richard Mille partner since 2010, said Hughes.

"When Richard Mille started the brand in 2001, he hated to see athletes only put on a watch just to get their trophy after they completed their sport," she explained. "He didn’t think that was very genuine. From the start, he only formed partnerships with athletes if they could wear the watch while they performed the sport."

That challenged the brand’s watchmakers to make a product that is comfortable enough for an athlete to wear in-game but also strong enough to be a precise timekeeper, Hughes said.

"For someone like [Nadal], it has to be super light and strong," she said. "He has his massive backhand, so we have to make sure it won't break the watch."

Richard Mille also partners with Formula One and IndyCar drivers, such as Simon Pagenaud, who won the Indy 500.

"They experience extreme G-forces when they drive, so their watches have to be able to endure those kind of shocks," said Hughes.

While Mille watches have been worn by drivers, tennis players and now even football players, the most intense sport for which its watches have to be prepared is polo.

"The watch must be able to survive strikes from a mallet, falling off a horse and getting stomped on by a horse," said Hughes.